Emissive cathode



July 31, 1956 J, KATZBERG 2,757,308

EMISSIVE CATHODE Filed Jan. 28, 1954 FIG. I

JESSE KATZBERG INVENTOR ATTORNEY United States Patent EMISSIVE CATHODE Jesse Katzberg, Tenafly, N. J., assignor, by mesne assignments, to Gera Corporation, New York, N. Y., a corporation of New Jersey Application January 28, 1954, Serial No. 406,720 3 Claims. (Cl. 313-345) This invention relates to emissive coatings for cathodes in discharge devices and has particular reference to an intermediate layer of bonding material which provides a secure anti-shock foundation between the cathode base electrode and the outer emissive coating.

Emissive coatings for electron discharge devices have been constructed by depositing the emissive coating directly on the surface of the metallic base electrode. Such an arrangement is generally good enough to provide a structure which performs well in all applications such as radio receiving sets, phonograph reproducers, and medium power transmitting applications. However, it has been found that in cases where discharge devices are subjected to severe shock, the emissive coating applied directly to the metal may become loose and fall off. The present invention provides a structure for emissive coatings which will withstand severe shocks and, in addition, includes other desirable features not found in the conventional type of cathode.

One of the objects of this invention is to provide an improved emissive coating which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to protect the cathode coating from becoming loose and falling off when the tube is subjected to severe shock.

Another object of the invention is to provide an emissive coating which will not sputter when subjected to severe ion bombardment in gas-filled discharge devices.

Another object of the invention is to increase the shock resistant qualities of cathode coatings without lowering the etficiency of the electron emission.

Another object of the invention is to provide an emissive coating for cathodes which can be used either in a highly exhausted vacuum tube or in a gas-filled discharge device.

One feature of the invention includes an intermediate coating of barium aluminate which is applied to the cathode electrode. The usual emissive coating of barium and strontium carbonates is deposited on the surface of the barium aluminate.

Another feature of the invention includes a first coating of a mixture of barium aluminate and the emissive carbonates and a second coating of the emissive carbonates alone.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

Fig. 1 is a plan view of a heater type cathode with parts cut away to show the internal construction.

Fig. 2 is a side view of a vacuum tube diode showing a filamentary cathode.

2,757,308 Patented July 31, 1956 Fig. 3 is a cross sectional view of the cathode shown in Fig. 1.

Fig. 4 is a cross sectional view of a filamentary type cathode.

Referring now to the drawings Figs. 1 and 3 show a cathode having a hollow cylindrical metal base 10 with a heater element 11 inserted in a hollow tubular cavity. A first coating of barium aluminate 12 (BaAlO4) is deposited on the metal base 10 and may be any thickness which produces the desired working characteristics. It has been found by experiment that a coating .0001 to .0005 inch is a satisfactory amount.

A second coating 13 composed of the usual mixture of barium and strontium carbonates is deposited on the surface of the barium aluminate. A small amount of binder material may be added to the mixture but for this type of cathode a binder is not necessary. The thickness of the emissive coating should conform to the usual practice in the manufacture of vacuum and gas tubes and may be of the order of ten milligrams of deposited material per square centimeter.

After the cathode is formed it is mounted in a vacuum tube and the usual baking out processes are applied. During the exhaust routine the deposited coatings are heated sufiiciently to produce a close adhering bond between the metal and the barium aluminate and between the barium aluminate and the emissive coating.

While the above described coatings have been found to be satisfactory and resistant to severe shocks, an alternate coating may be used which retains the shock resistant qualities and has more conductivity. This coating arrangement is the same as shown in Figs. 1 and 3 and described above but includes an intermediate binder material composed of a mixture of barium aluminate together with barium and strontium carbonates. Barium aluminate is itself emissive and its inclusion as a binder material does not reduce the efliciency of electron emission but does alter the mechanical strength of the cathode structure, causing it to adhere to the metallic base and to resist flaking and sputtering due to mechanical shock and ionic bombardment.

Figs. 2 and 4 show a diode vacuum tube having an envelope 15, an anode 16, and a filamentary cathode 17 which is coated with an emissive coating similar to the structure shown in Figs. 1 and 3. This cathode includes a filament element 18 which may be the usual tungsten or a wire made of an alloy of tungsten and molybdenum or any other filamentary material. The base filament material is coated with the barium aluminate 12 and an emissive coating 13 as described above.

It is well known that any emissive coating may be combined with a small percentage of a neutral binder material without effecting the efliciency of emission. In like manner barium aluminate may be combined wi small percentages of other neutral materials without effecting either its adhering or emissive qualities.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that various changes and modifications may be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

I claim:

1. A thermionic emissive electrode comprising, a conductive base, an intermediate coating on the base which includes barium aluminate, and an electron emissive substance on the barium aluminate.

2. A thermionic emissive electrode comprising, a con- 3 ductive filament with means for passing current therethrough, an intermediate coating on the filament which includes barium aluminate, and a mixture of electron emissive substances on the barium aluminate which includes barium carbonate and strontium carbonate.

3. A thermionic emissive electrode comprising, a conductive filament, conductive means secured to the ends of said filament for heating the filament to an emitting temperature, an intermediate coating on the filament which includes barium aluminate, and a mixture of electron emissive substances on the intermediate coating which includes barium carbonate and strontium carbonate.

References Cited in the file of this patent UNITED STATES PATENTS Bedford Aug. 8, 1933 Ramsay et al. June 29, 1937 Waldschrnidt Sept. 27, 1938 Kolligs et a1. Sept. 5, 1939 Lawton Feb. 25, 1947 

1. A THERMIONIC EMISSIVE ELECTRODE COMPRISING, A CONDUCTIVE BASE, AN INTERMEDIATE COATING ON THE BASE WHICH INCLUDES BARIUM ALUMINATE, AND AN ELECTRON EMISSIVE SUBSTANCE ON THE BARIUM ALUMINATE. 